Modulation to extend zero-voltage switching margin for dual-active bridge converter

1. A method comprising: detecting a bus voltage of a dual active bridge (DAB) converter, wherein the DAB comprises a primary bridge, a secondary bridge, and a transformer coupling the primary bridge to the secondary bridge; determining a first duty ratio of the primary bridge and a second duty ratio of the secondary bridge; modifying at least one of the first duty ratio and the second duty ratio by adjusting at least one of a differential mode (DM) adjustment variable and a common mode (CM) adjustment variable based on the detected bus voltage; and causing a plurality of switch control signals, which are provided to respective switches of the primary bridge and the secondary bridge, to switch according to a time-based switching sequence based on the first duty ratio and the second duty ratio.

2. The method of claim 1, wherein modifying at least one of the first duty ratio and the second duty ratio comprises modifying at least one of the first duty ratio and the second duty ratio such that a current of the transformer changes polarity before the secondary bridge switches off.

3. The method of claim 1, wherein: the DM adjustment variable is based on the detected bus voltage, a leakage inductance of the transformer, and a first gain; and the CM adjustment variable is based on a deadtime of the DAB converter and a second gain.

4. The method of claim 1, wherein the DM adjustment variable is a product of a first gain and a ratio of a leakage inductance of the transformer to the detected bus voltage.

5. The method of claim 1, wherein the CM adjustment variable is a product of a second gain and a dead time between interlocked switches of the primary bridge or the secondary bridge.

6. The method of claim 1, wherein the secondary bridge switches off before the primary bridge while a polarity of a current of the transformer is opposite to a polarity of a secondary bus voltage of the secondary bridge.

7. The method of claim 1, wherein modifying at least one of the first duty ratio and the second duty ratio comprises modifying at least one of the first duty ratio and the second duty ratio to avoid zero current switching (ZCS) of the DAB converter.

8. The method of claim 1, wherein modifying at least one of the first duty ratio and the second duty ratio comprises modifying at least one of the first duty ratio and the second duty ratio such that: at each rising edge of a primary side voltage of the transformer, a current of the transformer is negative; at each falling edge of the primary side voltage of the transformer, the current of the transformer is positive; at each rising edge of a secondary side voltage of the transformer, the current of the transformer is positive; and at each falling edge of the secondary side voltage of the transformer, the current of the transformer is negative.

9. The method of claim 1, wherein detecting the bus voltage comprises: detecting a primary bus voltage of the primary bridge; detecting a secondary bus voltage of the secondary bridge; and selecting, as the detected bus voltage, the bus voltage having smaller voltage fluctuations among the primary bus voltage and the secondary bus voltage.

10. A method comprising: detecting a bus voltage of a dual active bridge (DAB) converter, wherein the DAB comprises a primary bridge, a secondary bridge, and a transformer coupling the primary bridge to the secondary bridge; determining when to turn off the primary bridge and the secondary bridge based on the detected bus voltage such that zero voltage switching (ZVS) is achieved for one or more switches of the primary bridge and the secondary bridge, comprising: determining a differential mode (DM) adjustment variable and a common mode (CM) adjustment variable; and modifying at least one of a first duty ratio of the primary bridge and a second duty ratio of the secondary bridge based on the DM adjustment variable and the CM adjustment variable; and causing a plurality of switch control signals, which are provided to respective switches of the primary bridge and the secondary bridge, to switch according to a time-based switching sequence based on the determination of when to turn off the primary bridge and the secondary bridge.

11. The method of claim 10, further comprising switching off the secondary bridge before switching off the primary bridge.

12. A system for controlling a dual active bridge (DAB) converter having a primary bridge, a secondary bridge, and a transformer coupling the primary bridge to the secondary bridge, the system comprising: a port of the DAB converter; a plurality of output ports coupled to switches of the DAB converter; and control circuitry coupled to the port and the plurality of output ports and configured to: detect a bus voltage of the DAB converter via the port; determine a first duty ratio of the primary bridge and a second duty ratio of the secondary bridge; modify at least one of the first duty ratio and the second duty ratio by adjusting at least one of a differential mode (DM) adjustment variable and a common mode (CM) adjustment variable based on the detected bus voltage; and cause a plurality of switch control signals, which are provided to respective switches of the primary bridge and the secondary bridge, to switch according to a time-based switching sequence based on the first duty ratio and the second duty ratio.

13. The system of claim 12, wherein the control circuitry is configured to modify at least one of the first duty ratio and the second duty ratio by modifying at least one of the first duty ratio and the second duty ratio such that a current of the transformer changes polarity before the secondary bridge switches off.

14. The system of claim 12, wherein each of the switches of the DAB converter is a gallium nitride (GaN) based semiconductor or a silicon carbide (SiC) based semiconductor.

15. The system of claim 12, wherein: the DM adjustment variable is a product of a first gain and a ratio of a leakage inductance of the transformer to the detected bus voltage; and the CM adjustment variable is a product of a second gain and a deadtime between interlocked switches of the primary bridge or the secondary bridge.

16. The system of claim 12, wherein the secondary bridge switches off before the primary bridge while a polarity of a current of the transformer is opposite to a polarity of a secondary bus voltage of the secondary bridge.

17. The system of claim 12, wherein the control circuitry is configured to modify at least one of the first duty ratio and the second duty ratio by modifying at least one of the first duty ratio and the second duty ratio to avoid zero current switching (ZCS) of the DAB converter.

18. The system of claim 12, wherein the control circuitry is configured to modify at least one of the first duty ratio and the second duty ratio by modifying at least one of the first duty ratio and the second duty ratio such that: at each rising edge of a primary side voltage of the transformer, a current of the transformer is negative; at each falling edge of the primary side voltage of the transformer, the current of the transformer is positive; at each rising edge of a secondary side voltage of the transformer, the current of the transformer is positive; and at each falling edge of the secondary side voltage of the transformer, the current of the transformer is negative.

19. The system of claim 12, wherein the control circuitry is configured to detect the bus voltage by: detecting a primary bus voltage of the primary bridge; detecting a secondary bus voltage of the secondary bridge; and selecting, as the detected bus voltage, the bus voltage having smaller voltage fluctuations among the primary bus voltage and the secondary bus voltage.